A catalytic converter for purifying exhaust gases from an internal combustion engine of an automobile or the like is desired to be provided under a high-temperature condition to maintain exhaust-gas purification performance of a catalyst. For this reason, the catalytic converter comprises, for example, a heat insulating structure comprising an outer tube and an inner tube as disclosed in Patent Document 1 to enhance the heat retaining property in a housing tube where a catalyst carrier is housed.
FIG. 6 shows a schematic block diagram of a catalytic converter comprising a double tube having an outer tube and an inner tube. As shown in FIG. 6, a catalytic converter 100 comprises a cylindrical catalyst carrier 102 inside a catalyst housing tube 101 that has a tube-shape with reduced diameters at both ends. The catalyst carrier 102 is steadily held inside the catalyst housing tube 101 by the outer periphery of the catalyst carrier 102. An outer tube 104 is further provided outside the catalyst housing tube 101, the outer tube 104 having almost the same shape as the catalyst housing tube 101 and having a diameter larger than that of the catalyst housing tube 101.
As shown in FIG. 6, a heat insulating effect inside the catalyst housing tube 101 is enhanced by providing a space between the outer tube 104 and the catalyst housing tube 101; thus, a decrease in temperature inside the housing tube is reduced, and heat transfer to the outside of the housing tube is reduced.